Man's rate of consumption of hydrocarbon fuels far exceeds nature's rate of replenishment of these fuels via the carbon cycle, fossilization and geochemistry. The consequences of the worldwide combustion of hydrocarbon fuels are an increase in the concentration of carbon dioxide in the atmosphere along with a steady diminishing of hydrocarbon fuel reserves; both to the detriment of civilization.
A process that consumes water and carbon dioxide to produce hydrocarbons and oxygen and that is driven by a non-fossil based prime energy source would help to reverse the above-described trend and thus lessen man's dependence upon fossil-based fuels. Such a process would depend on nuclear fusion or fission reactors and/or direct solar energy for prime energy input.
Direct reaction of carbon dioxide with water to produce oxygen and hydrocarbons is thermochemically unfavorable. The Gibbs free energy of reaction is large and positive at all practical temperatures and as a consequence few direct synthesis reactions have been invented to date. The situation seems made to order for a two-reaction thermochemical cycle. Such a cycle consists of two thermochemically favorable reactions that sum to equal the direct production of oxygen and hydrocarbon fuels from carbon dioxide and water. Thermochemical cycles have been the subject of much research as applied, for example, to splitting of water into hydrogen and oxygen.
The present invention entails a two-reaction thermochemical cycle for producing oxygen and hydrocarbons from carbon dioxide and water. Vaporized water is reacted endothermically at high temperature with metal cations contained within porous solid zeolite material to produce oxygen gas and reduced metal cations and protons within the solid, porous zeolite material. The reduced cation and proton containing solid zeolite material is then cooled by regenerative heat exchange to a low reaction temperature. Carbon dioxide is reacted exothermically with the cooled down, zeolite-contained, reduced metal cations and protons to produce a product gas mixture of hydrocarbons and water along with zeolite-contained metal cations oxidized to their starting oxidation state. A cyclic process is described such that the solid zeolite metal-cation-containing material cycles between the two reaction zones. For maximum thermodynamic efficiency the above-mentioned regenerative heat exchange serves to retain within the process the intrinsic heat contained by the solid zeolite material while it is cooled down and then heated up in the sequential fashion described.
Because the high temperature endothermic reaction can be driven by any source of high temperature process heat, the invented process can be driven by such non-fossil-fuel-based energy sources as nuclear fission and fusion reactors and solar collectors and concentrators.